Method for obtaining a bright zinc coating by electrodeposition and the bath used therefor

ABSTRACT

A brightening composition and a process for electrodepositing of zinc is described herein. The brightening composition is the reaction product of an aromatic aldehyde and an amine of the formula H2NR wherein R is a saturated aliphatic hydroxyl radical having from one to four carbon atoms. In particular, bright deposits are achieved when an amide or substituted amide is intermixed with the reaction product of the aromatic aldehyde and the amine.

United States Patent METHOD FOR OBTAINING A BRIGHT ZINC COATING BYELECTRODEPOSITION AND THE BATH USED THEREFOR 16 Claims, No Drawings US.Cl 204/55 Int. Cl C23b 5/10, C23b 5/46 Field of Search 204/55,

[56] References Cited UNITED STATES PATENTS 2,734,026 2/1956 Chester204/44 2,315,802 4/1943 Lind et al.. 204/49 3,088,884 5/1963 Passal204/55 3,317,412 5/1967 Dahlmann 204/55 3,472,743 10/1969 Rushmere204/55 FOREIGN PATENTS 1,109,479 6/1961 Germany 204/55 PrimaryExaminerG. L. Kaplan Attorneys-Wayne C. Jaeschke, Martin Goldwasser andDaniel S. Ortiz ABSTRACT: A brightening composition and a process forelectrodepositing of zinc is described herein, The brighteningcomposition is the reaction product of an aromatic aldehyde and an amineof the formula H,NR wherein R is a saturated aliphatic hydroxyl radicalhaving from one to four carbon atoms. In particular, bright deposits areachieved when an amide or substituted amide is intermixed with thereaction product of the aromatic aldehyde and the amine.

METHOD FOR OBTAINING A BRIGHT ZINC COATING BY ELECTRODEPOSITION AND THEBATH USED THEREFOR BACKGROUND OF THE INVENTION In the art ofelectroplating, it is a practice to charge a cell with an electrolytehaving the particular metals to be plated dissolved therein. The cellsare equipped with anodes usually at each end thereof, with the materialto be plated sewing as the cathode. Thus, current flows therebetween todeposit the metal to be plated. Conventional solutions for theelectrodeposition of zinc can be classified into two categories. Thefirst category is the acid zinc baths, such as those containing zincsulphate, zinc chloride, zinc fluoborate and the like. The secondcategory is the alkaline zinc baths that contain zinc oxide, with andwithout sodium cyanide, and sodium hydroxide. The electrodeposit fromboth of these baths is generally dull without brightening agents. Theseagents are seldom suitable for baths of both categories.

The electrodeposition of zinc from alkaline cyanide zinc solutions iswidely used to produce coatings which protect iron or steel bysacrificial cathodic action. To improve this bath, brightening agentsare used. These agents impart to the electrodeposit metal a lustrousappearance. A wide variety of brightening agents have been successfullyused; however, inost have not been completely satisfactory. Some workwell for still plating while others are only successfully used in barrelplating. In addition, some brightener compositions are not stable in theplating bath. Other compositions, while yielding bright deposits, arenot suitable for accepting a chromate or phosphate protective film.Illustrative of these systems may be found in the following US. Pat.Nos. 2,740,754; 2,989,449; 3,088,884; 3,296,105; 3,317,412 and3,318,767.

The conventional baths for obtaining bright zinc coatings have a cyanidecontent from about to about 14 oz./gal. The removal of the poisonouscyanide waste from the rinse water effluent as required by governmentalregulations is excessively expensive. Therefore, it is desirable tooperate the zinc electroplating bath at a low cyanide content tominimize effluent treatment expenses. Moreover, the conventional zinccyanide baths have a short downtime life. For example, after a bathcontaining additives of the prior art is allowed to stand overnightwithout plating, about one-half of the initial charge of the additivemust be added to restore the deposit to its original degree ofbrilliance.

BRIEF DESCRIPTION OF THE INVENTION It has been discovered that certainwater-soluble reaction products of an aromatic aldehyde with aliphaticamines form complex chemical structures and provide bright deposits inzinc cyanide electrolytes with excellent downtime life. These complexesare fonned by adding predetennined amounts of aromatic aldehyde withalkanolamines to provide the structures of this invention. Inparticular, excellent brilliance is provided to the zinc deposits byemploying with the amine aldehyde complexes a water-soluble amide orsubstituted amide compound.

DETAILED DESCRIPTION OF THE INVENTION In the practice of the presentinvention, a brightener com pound is prepared by reacting an aromaticaldehyde with an amine having the formula H NR wherein R is a saturatedaliphatic hydroxyl radical wherein the aliphatic moiety can have fromone to four carbon atoms. The reaction of the two components ispreferably carried out in the presence of water. Thus, the aromaticaldehydes can be selected from a group consisting of anisic aldehyde,salicyclic aldehyde, tolyl aldehyde vanillin or other aromatic aldehydesconventionally used in cyanide baths. The aromatic aldehydes can befirst emulsified with the water to form an aromatic aldehyde wateremulsion. Thereafter, the alkanolamine is added thereto in an amount ofat least a stoichiometric quantity to react with the aromatic aldehyde.Preferably, up to about 60 percent excess of the amine can be used. Thereaction product of the aromatic aldehyde and the alkanolamine has shownto be an excellent brightening composition when used in a cyanide bath.

In its preferred form, the reaction product of the aromatic aldehyde andalkanolamines is manufactured by first adding the aromatic aldehyde toheated water to form an emulsion. The water temperature is then reducedand the alkanolamine is added which reacts exothermically with thearomatic aldehyde.

After the brightening composition has been manufactured, it is thenadded to a conventional cyanide bath consisting of sodium cyanide,sodium hydroxide and zinc. It has been found in practice that whenmetals are plated with the zinc solution contained in the brighteners ofthe present invention, a full bright and brilliant coating is obtained.Thus, the aldehyde amine composition can be present in an amount rangingbetween about 0.02 to about 0.3 grams per liter of the bath solution.

Furthennore, it has been discovered that even a brighter and morebrilliant zinc deposit can be obtained when a watersoluble amide orsubstituted amide compound is dissolved within the brightening solution.These compounds may be selected from the group consisting of:

wherein R and R, can each be selected from a group consisting ofhydrogen, saturated aliphatic radicals having from one to six carbonatoms, saturated hydroxyl substituted aliphatic radicals having from oneto six carbon atoms, and any mixtures thereof. Specific examples of theamide compounds within the scope of the above identified fonnulas arenicotinamide, N-hexylnicotinamide, N,N-diethylnicotinamide, N-ethylnicotinamide, N,N-di(2-hydroxylpropyl) nicotinamide,isonipecotamide, N-methylisonipecotamide and N- ethylolisonipecotamideand mixtures thereof. The amide composition can be present in an amountranging between about 0.0015 to about 0.14 grams per liter of the bathsolution.

It has been particularly noted that when the amide or substituted amidecomponent is incorporated within the brightener solution, considerablyless amount of sodium cyanide can be employed within the bath solution.It is preferred that from about 1 to about 10 grams of the brightener beadded per liter of bath solution.

In order to illustrate the merits of the present invention, the

following examples are provided.

Example I A brightener was prepared from the following formula:

Salicylnldehyde 200 g. Vanillin l0 g. Gelatin 200 g. Polyvinyl alcohol30 g. Z-aminoethanol 200 g. Water 3,3]0 g.

1.5 ml. of the above brightener was added to 1 liter of a standardcyanide zinc bath which had the following analysis:

Sodium cyanide I05 3.". Sodium hydroxide 86 gJl. Zinc 37 g.ll.

A bent panel was plated in this solution using rod agitation at 1 amp.for 10 minutes. The panel was full bright but not brilliant.

Example 2 0.04 g. of N-methylnicotinamide was added to the bath ofexample 1. A bent panel was plated in this solution using rod agitationat 1 amp. for 10 minutes. The panel was full bright and brilliant.

Example 3 The bath from example 2 was allowed to stand for 4 weekswithout plating. After this period of standing, a bent panel was platedusing the same plating conditions as in example 2. The brilliancy of theresulting plated panel was almost the equivalent of that in example 2.

Example 4 A brightener was prepared from the following formula:

Anisic aldehyde 200 g. Vanillin 5 g. Gelatin 200 g. Polyvinyl alcohol 30g. 3-amino-n-propanol 200 g. Water 3,3l5 g.

1.5 ml. of this brightener was added to 1 liter of a standard cyanidezinc bath. A bent panel plated from this solution using rod agitation at1.5 amps. was bright except for the extreme low current density areas.

Example 5 0.04 g. of N(Z-hydroxyethyl)isonipecotarnide was added to thebath of example 4. Ten %-inch hex nuts were plated in this solution in asmall barrel at 1.5 amps. for 20 minutes. The nuts were bright. Notrouble was experienced chromating the nuts under the normal chromatingcycle.

Example 6 0.05 g. of N-ethylnicotinamide was added to the solution ofexample 5, and more hex nuts were plated similarly to example 5. Thenuts appeared to be slightly brighter than those in example 5.

Example 7 A brightener was prepared containing the followingingredients:

Nicotinamide 2% Salicylaldehyde 5% Vanillin l.5% Gelatin 6%2-aminopropanol 5% Water 80.5%

Ten ml, of the above brightener was added to 1 gallon of a low-cyanidezinc bath which had the following analysis:

Zinc 9 g.ll. Sodium cyanide l l.5 g./l. Sodium hydroxide 79 g./l.

Forty /4X2O l-inch hexhead bolts were plated in a small laboratoryplating barrel. The barrel was plated at 5 amps. for one-half hour. Theplated zinc deposit on the bolts was bright and leveled. Five of thesebolts were chromated in an irridescent chromate. No difficulty was foundin obtaining the normal chromate film on the bolts provided that theywere rinsed thoroughly.

Example 8 Plating tests were continued on the bath of example 7. Thebrightener level was kept high enough so that full bright deposits wereobtained. The barrel tests were continued until a definite additionpattern was established. A consumption rate was calculated from thesetests. The addition rate established was 426 X cc. of thebrightener/1,000 amp. hr.

Example 9 A brightener was prepared with the following ingredients:

Salicylaldehyde 3% Anisic aldehyde 2% Vanillin 1.5% Gelatine 5%Polyvinyl alcohol 0.75% Z-Bminoethanol 5% Water 80.75%

Nicotinamide 2% When the 2-aminoethanol was added to the water emulsionof anisic aldehyde and salicylaldehyde, considerable heat was evolvedindicating that a reaction between the aldehydes and the 2-aminoethanoltook place.

Example 10 A standard cyanide zinc solution had the following analysis:

Sodium hydroxide 47 3.". Sodium cyanide 52.5 g./l. Zinc [6.5 g.ll.

Example I 1 Barrel tests continued on the bath of example 10. The sodiumcyanide content of this bath was allowed to drop and the sodiumhydroxide was increased while plating every day until the bath had thefollowing analysis:

Sodium hydroxide 78 g./l. Sodium cyanide l3.2 g.ll. Zinc 7.5 gJl.

Full bright deposits were obtained from this bath during this transitionperiod by the periodic addition of the brightener of example 9. At theend of this test full bright zinc plated deposits were still obtained.No difficulty was experienced in chromating the parts at any time. Theconsumption rate of the low cyanide bath was calculated to be 2liters/10,000 amp. hr.

What is claimed is:

1. In an aqueous, alkaline zinc cyanide plating bath, the improvementwhich comprises the presence in said bath of a brightener compositionwhich comprises a combination of: (1) the reaction product of at leastone aromatic aldehyde with at least a stoichiometric quantity of atleast one alkanolamine having the formula H NR wherein R is a saturatedaliphatic hydroxyl radical containing from one to four carbon atoms and(2) at least one water-soluble amide or substituted amide correspondingto the formula:

wherein R, and R can be the same or different and are selected from thegroup consisting of hydrogen, saturated aliphatic radicals containingfrom one to six carbon atoms and saturated hydroxyl substitutedaliphatic radicals containing from one to six carbon atoms; saidreaction produce being present in said bath in a concentration fromabout 0.02 to 0.3 grams per liter and said amide or substituted amidebeing present in a concentration of from about 00015 to 0.14 grams perliter.

2. The bath of claim 1, wherein said aromatic aldehyde is at least onemember selected from the group consisting of anisic aldehyde, vanillin.salicylic aldehyde and tolyl aldehyde.

3. The bath of claim 2, wherein said aromatic aldehyde is vanillin.

4. The bath of claim 1, wherein said amide or substituted amide is atleast one member selected from the group consisting of:

nicotinamide, N-hexylnicotinamide,

N,N-diethylnicotinamide, N-ethylolnicotinamide,

N-N-di( 2-hydroxypropyl)nicotinamide, isonipecotamide,

N-methylisonipecotamide, and N-ethylolisonipecotamide.

5. The bath of claim 4, wherein said amide or substituted amide isnicotinamide.

6. The bath of claim 1, wherein polyvinyl alcohol is also presenttherein.

7 7. The bath of claim 1, wherein gelatine is also present therein.

8. The bath of claim 1, wherein both polyvinyl alcohol and gelatine arealso present therein.

9. In the process of electrodepositing zinc from an aqueous, alkalinezinc cyanide plating bath, the improvement which comprises adding to thebath a brightener composition which comprises a combination of: (l) thereaction product of at least one aromatic aldehyde with at least astoichiometric quantity of at least one alkanolamide having the formulaH,NR wherein R is a saturated aliphatic hydroxyl radical containing fromone to four carbon atoms and (2) at least one water-soluble amide orsubstituted amide corresponding to the formula:

wherein R and R can be the same or difierent and are selected from thegroup consisting of hydrogen, saturated aliphatic radicals containingfrom one to six carbon atoms and saturated hydroxyl substitutedaliphatic radicals containing from one to six carbon atoms; saidreaction product being present in said bath in a concentration of fromabout 0.02 to 0.3 grams per liter and said amide or substituted amidebeing present in a concentration of from about 0.0015 to 0.14 grams perliter.

10. The process of claim 9, wherein said aromatic aldehyde is at leastone member selected from the group consisting of anisic aldehyde,vanillin, salicylic aldehyde and tolyl aldehyde.

11. The process of claim 10, wherein said aromatic aldehyde is vanillin.

12. The process of claim 9, wherein said amide or substituted amide isat least one member selected from the group consisting of:

nicotinamide, N-hexylnicotinamide.

N,N-di( 2-hydroxypropyl)nicotinamide, isonipecotamide,

N,N-di(2hydroxypropyl)nicotinamide, isonipecotamide,

N-methylisonipecotamide, and N-ethylolisonipecotamide.

13. The process of claim 9, wherein said amide or substituted amide isnicotinamide.

14. The process of claim 9, wherein polyvinyl alcohol is also present insaid bath.

[5. The process of claim 9, wherein gelatine is also present in saidbath.

16. The process of claim 9, wherein both polyvinyl alcohol and gelatineare also present in said bath i i 3 i "H050 UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent 5,620,938 Dated November 16, 1971Inventods) James A. Von Pless and Richard P. Cope, Jr.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 5, Example 7, line 55, after "ml the comma should be a--period--.

Column line 2, after "#26" delete the g.

Column 5, line 2, the Word "produce" should read product--;

line 3, after the word "concentration" insert Column 6, Claim 12, line6, delete "N,N-di(2hydroxypropyl)- nicotinamide, isonipecotamide" andinsert --N,N-diethylnicotinamide, N-ethylolnicotinamide-- Signed andsealed this 27th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSGHALK Attesting Officer Commissionerof Patents

2. The bath of claim 1, wherein said aromatic aldehyde is at least onemember selected from the group consisting of anisic aldehyde, vanillin,salicylic aldehyde and tolyl aldehyde.
 3. The bath of claim 2, whereinsaid aromatic aldehyde is vanillin.
 4. The bath of claim 1, wherein saidamide or substituted amide is at least one member selected from thegroup consisting of: nicotinamide, N-hexylnicotinamide,N,N-diethylnicotinamide, N-ethylolnicotinamide,N,N-di(2-hydroxypropyl)nicotinamide, isonipecotamide,N-methylisonipecotamide, and N-ethylolisonipecotamide.
 5. The bath ofclaim 4, wherein said amide or substituted amide is nicotinamide.
 6. Thebath of claim 1, wherein polyvinyl alcohol is also present therein. 7.The bath of claim 1, wherein gelatine is also present therein.
 8. Thebath of claim 1, wherein both polyvinyl alcohol and gelatine are alsopresent therein.
 9. In the process of electrodepositing zinc from anaqueous, alkaline zinc cyanide plating bath, the improvement whichcomprises adding to the bath a brightener composition which comprises acombiNation of: (1) the reaction product of at least one aromaticaldehyde with at least a stoichiometric quantity of at least onealkanolamine having the formula H2NR wherein R is a saturated aliphatichydroxyl radical containing from one to four carbon atoms and (2) atleast one water-soluble amide or substituted amide corresponding to theformula: wherein R1 and R2 can be the same or different and are selectedfrom the group consisting of hydrogen, saturated aliphatic radicalscontaining from one to six carbon atoms and saturated hydroxylsubstituted aliphatic radicals containing from one to six carbon atoms;said reaction product being present in said bath in a concentration offrom about 0.02 to 0.3 grams per liter and said amide or substitutedamide being present in a concentration of from about 0.0015 to 0.14grams per liter.
 10. The process of claim 9, wherein said aromaticaldehyde is at least one member selected from the group consisting ofanisic aldehyde, vanillin, salicylic aldehyde and tolyl aldehyde. 11.The process of claim 10, wherein said aromatic aldehyde is vanillin. 12.The process of claim 9, wherein said amide or substituted amide is atleast one member selected from the group consisting of: nicotinamide,N-hexylnicotinamide, N,N-diethylnicotinamide, N-ethylolnicotinamide,N,N-di(2-hydroxypropyl)nicotinanide, isonipecotamide,N-methylisonipecotamide, and N-ethylolisonipecotamide,
 13. The processof claim 9, wherein said amide or substituted amide is nicotinamide. 14.The process of claim 9, wherein polyvinyl alcohol is also present insaid bath.
 15. The process of claim 9, wherein gelatine is also presentin said bath.
 16. The process of claim 9, wherein both polyvinyl alcoholand gelatine are also present in said bath.